1. Field of the Invention
The present invention broadly relates to bandpass filters and, more particularly, is concerned with the provision of a bandpass filter from a serial arrangement of reflection gratings operating in a Wood's anomaly region.
2. Description of the Prior Art
Filters are an important part of optical and electro-optical technology. They control spectral energy in applications ranging from spectrometry to optical communication systems.
U.S Pat. No. 2,945,953 to Martin discloses an arrangement of multiple gratings and mirrors for performing a filtering function in an infrared monochromotor. Harrison and Stroke in an article entitled "Attainment of High Resolution with Diffraction Gratings and Echelles" (Journal of the Optical Society of America, Dec. 1960, vol. 50, No. 12, pp. 1153-1158) propose an experimental spectrograph setup in which two echelles are arranged in series for performing a filtering function. Stroke and Stroke in an article entitled "Tandem Use of Gratings and Echelles to Increase Resolution, Luminosity, and Compactness of Spectrometers and Spectrographs," (Journal of the Optical Society of America, Mar. 1962, vol. 53, no. 3, pp. 333-338) trace the history of the use of tandem (series) arrangements of spectroscopic elements and report experimental results using two gratings in tandem in spectrograph arrangements. U.S. Pat. No. 4,088,884 to Rast et al discloses a filter having a serial arrangement of mirrors used in an optical communication system.
While the filter arrangements of the aforementioned patents and publication may satisfactorily perform their intended functions in the specific applications for which they were designed, a need exists for a bandpass filter having broader, more generalized, application and utility.